Conventionally, there is an Audio/Visual (AV) system in which a video recording and reproduction apparatus such as a Digital Versatile Disc (DVD) recorder is connected to a television receiver (hereafter referred to as “TV”). In the AV system, video and audio are viewed, and an external AV amplifier and an external speaker are further connected to output audio from the external speaker. In order to view and operate each apparatus in such an AV system, the user needs to perform an operation of input selection or reproduction by separately using a remote controller (hereafter referred to as “remote control”) corresponding to the apparatus. This requires a complex operation.
One method for solving this problem is a method that employs a High-Definition Multimedia Interface (HDMI) standard. In HDMI, a feature named Consumer Electronics Control (CEC) is defined (Non-patent Reference 1). CEC is a feature that connects a TV and various AV apparatuses by HDMI cables, and controls the AV apparatuses using CEC commands which enable bidirectional control command transmission and reception, via CEC buses included in the HDMI cables.
Moreover, the HDMI standard has a feature that a reproduction apparatus such as a DVD recorder can read reproduction capability information of a connected apparatus to adapt video and audio data to an output format of the connected apparatus or encrypt the video and audio data, and transmit the video and audio data.
For example, reproduction capability information is transferred from an apparatus (hereafter referred to as “HDMI input apparatus”) including a HDMI input unit, such as a TV or an AV amplifier, to an apparatus (hereafter referred to as “HDMI output apparatus”) to which the HDMI input apparatus is connected, using a Display Data Channel (DDC) bus that is a unidirectional connection. “DDC” mentioned here is a standard created by the Video Electronics Standards Association (VESA) as a feature of communicating model information and the like of a display to the HDMI output apparatus, in order to achieve plug and play for the display. Information transferred by DDC includes model information and a reproducible image and audio format of the HDMI input apparatus, a physical address assigned to the HDMI apparatus, and so on.
In the HDMI standard, a logical address (hereafter “LA”) and a physical address (hereafter “PA”) are defined for each apparatus, for communication by CEC commands.
A PA is an address determined so as to reflect a connection topology of the HDMI output apparatus, and is unidirectionally transmitted from the HDMI input apparatus to the HDMI output apparatus. The PA is determined by adding a value that differs for each HDMI input unit, to a PA obtained by the HDMI input apparatus.
An apparatus that includes both a HDMI input unit and a HDMI output unit, such as an AV amplifier, obtains a PA of the AV amplifier itself from an apparatus to which the HDMI output unit is connected. The AV amplifier then adds a value corresponding to the HDMI input unit to the obtained PA, thereby determining a PA of a HDMI output apparatus connected to the AV amplifier. Accordingly, a PA of an apparatus (hereafter “root apparatus”) that includes a HDMI input unit and serves as a root is determined hierarchically as “0. 0. 0. 0”.
For instance, a TV that Includes no HDMI output unit and only includes a HDMI input unit always has the PA “0. 0. 0. 0”, as a root apparatus. A PA of an apparatus connected to the root apparatus is determined in such a manner that, as an example, a PA of an apparatus connected to a first HDMI input unit of the root apparatus is “1. 0. 0. 0” and a PA of an apparatus connected to a second HDMI input unit of the root apparatus is “2. 0. 0. 0”.
An apparatus that includes both an input unit and an output unit further determines a PA for each input unit, from a PA of the apparatus itself. As an example, a PA of an apparatus connected to a first input unit of the apparatus having the PA “1. 0. 0. 0” is “1. 1. 0. 0”, and a PA of an apparatus connected to a second input unit of the apparatus having the PA “1. 0. 0. 0” is “1. 2. 0. 0”.
On the other hand, a LA is assigned to each CEC-capable apparatus connected via HDMI, and used as a destination address for CEC command transmission and reception.
In CEC, there are a command that is transmitted to a designated destination, and a broadcast command that is notified to all CEC-capable apparatuses connected via HDMI. Communication is performed by combining these commands in CEC.
Note that a CEC command is made up of a LA of a transmitter apparatus, a LA of a destination apparatus, an opcode, and an operand.
Furthermore, HDMI defines control commands such as <Active Source> for performing input selection, <Standby> for powering OFF an apparatus, <Give Power Status> for querying a power state of an apparatus, <Polling Message> for ascertaining whether or not an apparatus of a destination LA is present on a communication network, and <Vendor Command> enabling each manufacturer to independently define an apparatus operation. In HDMI, various cooperative operations can be realized by transmitting and receiving these control commands in combination between CEC-capable apparatuses connected via HDMI.    Non-patent Reference 1: High-Definition Multimedia Interface Specification Version 1.3a